Apparatus and method for cleaning hvac cooling coils

ABSTRACT

An apparatus for cleaning an HVAC coil unit comprises a supply and collection assembly with a housing defining an interior space for containing a quantity of cleaning solution. A pump has an inlet positioned to be in fluid communication with the cleaning solution and is operative to deliver the cleaning solution to an outlet of the supply and collection assembly in a volume of at least 40 gallons per minute. Fluid return piping defines a conduit to conduct used cleaning solution from the HVAC coil unit back to a collection inlet. A filter assembly is positioned along the fluid return piping to filter the used cleaning solution. A fluid flow device is operative to provide pressure to move a quantity of the used cleaning solution through the fluid return piping. The used cleaning solution is returned to the interior space through the collection inlet during operation of said fluid flow device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending application Ser. No.17/954,727, filed Sep. 28, 2022, which is a division of application Ser.No. 16/745,253, filed Jan. 16, 2020, now U.S. Pat. No. 11,486,663, whichis a continuation of application Ser. No. 15/392,885, filed Dec. 28,2016, now U.S. Pat. No. 10,539,381, which is based upon and claims thebenefit of the following provisional applications: Ser. No. 62/271,839,filed Dec. 28, 2015; Ser. No. 62/280,970, filed Jan. 20, 2016; and Ser.No. 62/340,277, filed May 23, 2016. Each of the foregoing applicationsis incorporated herein by reference in its entirety for all purposes.

BACKGROUND OF THE INVENTION

The present invention relates to HVAC (heating, ventilation, and airconditioning) systems, particularly those having cooling coils withclosely spaced and deep fin arrangements. More particularly, the presentinvention relates to a novel apparatus and method for cleaning HVACcooling coils.

HVAC cooling coils are designed to cool air by removing water or watervapor from the air passing across the coils. If the air passing acrossthe coils contains any contamination, the contamination will build upbetween the thin, closely aligned fins of the coils. (The fins maytypically be made of aluminum but they can be copper, stainless steel,or other suitable material.) As this contamination builds up, severalharmful things begin to happen. The contamination build-up startsinsulating the fins which progressively lowers the thermodynamic heattransfer properties of the entire system. The space between the coilsalso becomes narrower thereby restricting airflow in the system. Thisrestricted airflow builds pressure in the HVAC system and forces the fanmotor to work harder and/or reduces the output of air to the airconditioned spaces fed by the HVAC system. At some point, the buildup ofcontamination can make the HVAC system not function properly or at all.In a chilled water system, contamination buildup reduces the coil'sability to transfer heat, so the chiller that supplies the hot or coldwater has to work harder, thus using more energy. In a DX HVAC system,partially contaminated coils create an increased head pressure on thecompressor, making it run at an elevated temperature, which greatlyreduces the life of the compressor. The compressor is often the mostexpensive component in an HVAC system.

Contamination build-up on HVAC system coils can result in theintroduction and growth of microbiological organisms (microbials) suchas bacteria and fungi (mold). Microbials are ubiquitous in theenvironment and are brought into the HVAC system through fresh air ormake-up air intakes of the system. The microbials in the air arecaptured in the coils and are introduced into a moist environment withnutrients from built-up contaminants. Since the coils stay moist forlong periods of time, the mold and bacteria are allowed to grow. Thisbuildup of microbial growth in coils is commonly referred to as biofilm.When the temperature coming into the system is hot or warm, biofilmgrowth can take place rapidly. As coils dry out the mold and bacteriacan be released into the air in the occupied building through the HVACduct systems downstream of the coils. Microbials can cause serioushealth issues to building occupants. Health care facilities are at riskfrom these airborne microbials due to immunocompromised patients beingtreated in their buildings.

HVAC coils are supposed to be cleaned routinely to prevent and/or removecontamination build-up that causes the problems outlined above. Ifcleaning completely removes all contamination without damaging the finsof the coils and the HVAC ductwork also remains clean and dry, the HVACsystem would continue to perform as designed without introducingmicrobials into the building.

The typical procedure for cleaning HVAC coils is to use a pump-upsprayer to apply coil cleaner solution to the upstream and downstreamfaces of the coil. The cleaner is allowed to stay on the coil for theamount of time recommended by the coil cleaner manufacturer. A gardenhose or low pressure sprayer is then used to rinse the coils to removecontaminants from the cooling coil, as well as the coil cleaningchemicals.

Thus, conventional coil cleaning procedures use a garden hose supplyingapproximately 5-9 gallons per minute flow rate to flush the coil. Forthick coils (normally 4″ or greater), or closely spaced coil fins (morethan 10 fins per inch), such flow rates can only physically reach a fewinches into the cooling coil. Generally, when a thick coil (e.g., eightinches thick or more) is cut so that its cross-section can be inspected,the center of the coil is still impacted with contaminants that theconventional coil cleaning process cannot reach.

The present invention recognizes the foregoing considerations, andothers, of the prior art.

SUMMARY OF THE INVENTION

The present invention provides a novel apparatus and method for cleaningHVAC cooling coils to remove contaminants that have built up between thefins of the cooling coils. Preferred embodiments use a higher velocityflow of cleaning solution augmented with a flow of air (or othersuitable gas) to remove contaminants that cannot be removed withconventional coil cleaning systems and procedures. An apparatus andmethod in accordance with this invention will generally reach muchdeeper into the coil and substantially completely remove the buildup.Preferably, the cleaning solution is continuously removed as it collectsin a drain basin under the coils for use in enclosed spaces and tofacilitate cleanup.

One aspect of the present invention provides an apparatus for cleaningHVAC cooling coils. The apparatus comprises a supply and collectionassembly having a housing defining an interior space for containing aquantity of cleaning solution. A pump is also provided, having a pumpinlet positioned to be in fluid communication with the cleaningsolution. The pump is operative to deliver the cleaning solution to asupply outlet of the supply and collection assembly. A vacuum source hasa vacuum inlet positioned to be in fluid communication with an ullagespace such that the vacuum source creates negative pressure in theullage space during operation. A collection inlet is in fluidcommunication with the ullage space such that the cleaning solution isreturned to the interior space through the collection inlet duringoperation of the vacuum source.

Preferred embodiments of the apparatus further comprise a nozzle devicein fluid communication with the supply outlet via outlet piping which isconfigured to deliver the cleaning solution to a surface of an HVAC coilunit. Embodiments may also preferably include a fluid return tool influid communication with the collection inlet via return piping, thefluid return tool being configured to collect used cleaning solutionfrom the HVAC coil unit. Preferably, a filter assembly may be positionedalong the return piping between the fluid return tool and the collectioninlet.

For example, the filter assembly may comprise a hydrocyclonic filter. Insome such embodiments, an electrically-controlled flush valve may beprovided in fluid communication with a collection container of thehydrocyclonic filter. Control circuitry operative to open and close theflush valve so as to empty the collection container may also beprovided.

Many embodiments of the apparatus may further comprise air supply pipingconfigured to introduce compressed air into the cleaning solution beingdelivered from the supply outlet. An electrically controlled valve maybe situated in the air supply piping, the valve being operative topulsate introduction of the air into the cleaning solution at apredetermined frequency.

According to some preferred embodiments, upper and lower level switchesmay be provided in the interior space of the housing. The upper levelswitch is preferably operative to cut off power to the pump if athreshold upper level of the cleaning solution is reached. The lowerlevel switch is preferably operative to open a fresh water supply portif a threshold lower level of the cleaning solution is reached. The pumpmay be located entirely within the housing of the supply and collectionassembly. The vacuum source may comprises a motor located external tothe housing of the supply and collection assembly.

Another aspect of the present invention provides an apparatus forcleaning HVAC cooling coils. The apparatus comprises a supply andcollection assembly having a housing defining an interior space forcontaining a quantity of cleaning solution. A pump is operative todeliver the cleaning solution to a supply outlet of the supply andcollection assembly. A vacuum source is also provided having a vacuuminlet positioned to be in fluid communication with an ullage space suchthat the vacuum source creates negative pressure in the ullage spaceduring operation to return the cleaning solution through a collectioninlet.

The apparatus of this aspect further has a nozzle device in fluidcommunication with the supply outlet via outlet piping, the nozzledevice being configured to deliver the cleaning solution to a surface ofan HVAC coil unit. A fluid return tool is in fluid communication withthe collection inlet via return piping, the fluid return tool beingconfigured to collect used cleaning solution from the HVAC coil unit. Afilter assembly is in line with the return piping between the fluidreturn tool and the collection inlet.

According to some preferred embodiments, the nozzle device comprises adelivery face having a substantially planar surface for juxtaposition onthe surface of the HVAC coil unit, a plurality of apertures beingdefined in the delivery face for passage of the cleaning solution.Preferably, the apertures may be oriented at a predetermined anglerelative to the substantially planar surface of the delivery face. Insome embodiments, this predetermined angle may fall within a range ofapproximately 45 degrees to approximately 53 degrees.

A still further aspect of the present invention provides a method ofcleaning an HVAC coil unit located above a drain basin. One step of themethod involves providing a supply and collection assembly having areservoir containing liquid cleaning solution, a pump operative tooutput the liquid cleaning solution through a supply outlet, and avacuum source operative to draw in used liquid cleaning solution througha collection inlet. According to another step, a nozzle device in fluidcommunication with the supply outlet is also provided, the nozzle devicehaving a delivery face. A further step involves providing a fluid returntool in fluid communication with the collection inlet, and positioningthe fluid return tool in the drain basin. According to a further step,the delivery face of the nozzle device is moved across a surface of theHVAC coil unit to deliver the cleaning solution into areas between finsthereof.

Other objects, features and aspects of the present invention areprovided by various combinations and subcombinations of the disclosedelements, as well as methods of practicing same, which are discussed ingreater detail below.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, to one of ordinary skill in the art, is set forthmore particularly in the remainder of the specification, includingreference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of an HVAC cooling coil cleaningapparatus in accordance with an embodiment of the present invention.

FIG. 2 is a diagrammatic representation showing internal components ofthe supply and collection assembly of FIG. 1 .

FIGS. 3-5 are perspective views of an exemplary supply and collectionassembly in accordance with an embodiment of the present invention.

FIG. 5A is an enlarged perspective view of the control panel shown inFIG. 5 .

FIGS. 6A and 6B are perspective views of the exemplary supply andcollection assembly of FIGS. 3-5 with the outer casing removed to showninternal details.

FIGS. 7-8 are wiring schematics of control circuitry for the exemplarysupply and collection assembly of FIGS. 3-5 .

FIG. 9 shows a pulse control module (PCM) and related circuitry for thecompressed air pulsation valve.

FIGS. 10-11 are perspective views of an exemplary cyclonic filterassembly in accordance with an embodiment of the present invention.

FIG. 12 is a wiring schematic of control circuitry for the exemplarycyclonic filter assembly of FIGS. 10-11 .

FIG. 13 is an elevational view of an exemplary fluid return tool thatmay be used with embodiments of the present invention.

FIG. 14 is a partially diagrammatic elevational view of an exemplaryfluid delivery nozzle that may be used with embodiments of the presentinvention.

FIGS. 14A and 14B show front side and back side views, respectively, ofan exemplary face plate of the fluid delivery nozzle of FIG. 14 .

FIG. 15 is a diagram showing channel isolation in accordance withexemplary methodology of the present invention.

Repeat use of reference characters in the present specification anddrawings is intended to represent same or analogous features or elementsof the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

It is to be understood by one of ordinary skill in the art that thepresent discussion is a description of exemplary embodiments only, andis not intended as limiting the broader aspects of the presentinvention, which broader aspects are embodied in the exemplaryconstructions.

FIG. 1 illustrates an exemplary apparatus 10 in accordance with anembodiment of the present invention for cleaning an HVAC coil unit 12(labeled “heat exchanger”). As noted above, coil unit 12 may have alarge number of closely-spaced fins (e.g., at least 10 fins per inch)between which various contaminants will collect. Due to the depth ofcoil unit 12 (e.g., at least four inches), conventional cleaningtechniques have often been ineffective to clean the entire finstructure. A conventional drain pan 14 is located below coil unit 12, asshown.

Apparatus 10 includes a supply and collection assembly 16, preferably inthe form of an integrated unit (which may resemble, for example, abarrel). Supply and collection assembly 16, which will be referred toherein as “main assembly 16,” contains a quantity of cleaning solutionthat is supplied to and collected from coil unit 12 during the cleaningprocess. In this regard, main assembly 16 defines an internal space inwhich the cleaning solution is contained. The cleaning solution itselfmay preferably comprise a mixture of fresh water and one or moresuitable cleaning agents, such as detergents.

As will be explained, the cleaning solution is supplied via an outlet 18(labeled “OUT”) to clean the fins of coil unit 12. Recirculated solutionis drawn back into main assembly 16 via a return inlet 20 (labeled“IN”). Fresh water is added to main assembly 16 (at the beginning of thecleaning process or as water is lost during the cleaning process) via awater supply inlet 22 (labeled “WATER IN”). The water supply inlet, forexample, may comprise a common hose fitting to which a flexible hose canbe attached to connect it to a common water supply spigot. A drain 24 isprovided, preferably near the bottom of main assembly 16, for removal ofused cleaning solution at the conclusion of the cleaning process.

A nozzle device 26 is used to apply the cleaning solution under pressureto at least one of (and preferably both of) the front and back surfacesof coil unit 12. For example, the cleaning solution may be applied in aslow sweeping motion across the surface of coil unit 12. (In many cases,this sweeping motion will be done manually by an operator, althoughembodiments are contemplated in which a robotic mechanism may beemployed to move nozzle 26 in an automated fashion.) The sweeping motionmay preferably be horizontal, starting at the top of the coil unit'ssurface and proceeding to the bottom in successive courses. Cleaningsolution and the material that it removes from the fins will flow intothe drain pan 14 for collection. Nozzle device 26 preferably has amanual valve 28 associated therewith that the operator can close to stopflow of cleaning solution as necessary or desired.

As can be seen, nozzle device 26 is in fluid communication with outlet18 via suitable piping, at least some of which will take the form of aflexible hose 30 allowing movement of nozzle device 26 as described. Inaddition, a supply of compressed air is preferably combined with thecleaning solution at piping junction 32, as shown. In this regard, theair supply conduit 34 preferably has a valve 36 which can be used tointerrupt the supply of air. Preferably, valve 36 may take the form of asolenoid-controlled valve under the operation of the control circuitryof main assembly 16. The compressed air may be provided by a common aircompressor, or the facility in which coil unit 12 is located may have anintegrated compressed air supply.

In order to most effectively clean coil unit 12, apparatus 10 willdeliver a relatively large quantity of cleaning solution during thecleaning process. For example, some embodiments will provide between40-70 gallons of liquid per minute through a 1.5-inch inner diameter(ID) hose at approximately 40-80 psi of pressure. The compressed air,which may typically be between 80 and 120 psi, is injected into thecleaning solution stream via operation of valve 36. Preferably, valve 36may alternately open and close, so that the compressed air will beintroduced in a pulsating manner. For example, valve 36 may operate at apulse rate of between 0 Hz and 36 Hz in some presently preferredembodiments. A nominal pulse rate of approximately 22.7 Hz may beespecially desirable in some cases. A pulsating valve may also belocated just downstream of piping junction 32 to further pulsate thecombination of cleaning solution and injected air.

As shown, nozzle device 26 may be equipped with a deflector shield 38installed around its fluid outlet to keep the cleaning fluid fromgetting splashed onto the operator. In addition, deflector shield 38will desirably redirect “splash” water reflected off the coil unit'ssurface back onto and into the space between the fins. Specifically,deflector shield 38 may create a positive pressure in the area betweenthe shield and the coils which helps direct the cleaning liquid into thecoils, increasing the energy available to remove particles from the areabetween the coils. Preferably, deflector shield 38 will be flexible andhave the ability to slide across the fins' surface (i.e., the surfaceformed by the ends of the fins) without damaging them. For example, thedeflector shield may be formed of a suitable plastic material such aspolypropylene. While the deflector shield in the diagrammaticrepresentation of FIG. 1 is shown having flanges above and below thenozzle, one skilled in the art will appreciate that typically the flangewould be a continuous structure extending all the way around the nozzleto minimize escape of the cleaning fluid.

The recirculated cleaning solution is returned to main assembly 16 fromdrain pan 14, as noted above. In normal use, drain pan 14 is capable ofhandling a relatively small amount of condensate (e.g., 1 gpm or less).Thus, main assembly 16 provides substantial suction to remove thecleaning solution as it accumulates in drain pan 14. In this regard, asuction nozzle, referred to herein as “fluid return tool” 40, may beplaced in drain pan 14 to facilitate removal of the cleaning solution.Fluid return tool 40 may be attached to one end of a flexible hose 42,the other end of which is attached to the inlet port of a suitablefilter assembly 44. The outlet port of filter assembly 44 is in fluidcommunication with collection inlet 20 via suitable piping 46 (e.g., aflexible hose).

Preferably, filter assembly 44 is configured to remove particulate inthe cleaning solution. As will be explained more fully below, filterassembly 44 may take the form of a hydrocyclonic filter that separatesparticulate from liquid through centrifugal action. Material removed inthis manner collects in a container from which it can be removedmanually, or automatically through a flushing process. In theillustrated embodiment, a prefilter (i.e., a gross filter) mayoptionally be provided to remove larger particulates. For example, theprefilter may comprise a filter media 48 (e.g., polyester roll media)placed manually around the base of coil unit 12 before the cleaningprocess is begun.

Referring now to FIG. 2 , additional details of main assembly 16 can bemost easily explained. As shown, main assembly 16 comprises a housing 50defining an interior space. The interior space is partially filled witha cleaning solution 52 (“cleaning mixture”) such that an ullage 54exists above the upper surface of cleaning solution 52. Duringoperation, a vacuum source 56 creates negative pressure in the ullage 54(which is thus referred to as a “vacuum chamber”) to return usedcleaning solution back into housing 50 through collection inlet 20. Inthis case, for example, vacuum source 56 has an air inlet 58 in fluidcommunication with the ullage 54. Air is thus drawn by vacuum source 56from the interior space and exhausted to ambient. The size and power ofvacuum source 56 determines the rate at which cleaning solution isreturned to the housing 50. One skilled in the art will be able todetermine the appropriate vacuum source 56 to use in a particularapplication, depending on various factors. It will be appreciated thatthe motor/blower components of a wet-dry vacuum (which are widelyavailable) can be used for vacuum source 56. For example, vacuum source56 may comprise a NIKRO model no. DP55110.

Cleaning solution is pumped through outlet 18 by a pump, which in thiscase comprises a submersible pump 60 located adjacent the bottom of theinterior space of housing 50. The cleaning solution is drawn into pump60 through an inlet 62 located below the lowest permitted level ofcleaning solution. The cleaning solution is then pushed by pump 60 intopiping 64, which is in fluid communication with outlet 18. A suitablecheck valve 66 is positioned along piping 64 to prevent back flow intopump 60. As shown, outlet 18 is located at the top of housing 50 in thiscase.

Thus, cleaning solution 52 is continuously pumped during operationthrough outlet 18 and returned into housing 50 through inlet 20.Although some cleaning solution is inevitably lost at coil unit 12, ageneral equilibrium is achieved by this recirculation process.Nevertheless, the level (i.e., amount) of cleaning solution in housing50 should remain between certain thresholds in order to prevent damageto vacuum source 56 and/or pump 60, or to otherwise ensure properoperation of main assembly 16. In this regard, upper and lower floatswitches 68 and 70 are preferably located in the interior space ofhousing 50. Although different logical arrangements are contemplated,float switch 68 in this case moves away from its contact when the levelof cleaning solution rises to an upper threshold. The control circuitryresponds by discontinuing the operation of pump 60 (and optionallyvacuum source 56) until corrective action can be taken. (In addition, asone skilled in the art will appreciate, vacuum source 56 may have itsown integrated float switch.) Float switch 70 makes contact when thelevel of cleaning solution drops to a lower threshold, which opens awater valve to allow introduction of additional fresh water.

At the conclusion of the cleaning operation, the used cleaning solutionis drained from housing 50 via drain 24, which may take the form of acommon spigot or the like. For example, the cleaning solution may beallowed to flow into a floor drain or may be collected into suitablevessels for subsequent disposal. As shown, drain 24 is preferablylocated just above the lowest portion of a sloped floor 72 inside theinterior space of housing 50. Once the cleaning solution is drained,housing 50 may be refilled to an operating level with clean water. Atthat point, the same system may be used to perform a final rinse of thecoils with clean water to remove any residual chemicals or contaminantsstill in the coils.

Referring now to FIGS. 3 and 4 , main assembly 16 is preferablyconfigured to facilitate its movement from place to place. For example,housing 50 may in one preferred embodiment be attached to a standardhand truck 74, such as by retaining bands 76 and 78. Hand truck 74 has apair of wheels, such as wheel 80, by which main assembly 16 may beeasily moved into position near a coil unit to be cleaned. Hand truck 74also provides a platform for mounting of other aspects of main assembly16, such as the respective ports 82 and 84 (which may be suitablequick-connect ports) to which compressed air and fresh water connectionsare made. Also shown is the conduit 86 through which water flows intothe housing 50 from the port 84 when flow is permitted by a solenoidvalve 87 (FIG. 1 ). In addition, as shown in FIG. 5 , cord wraps may bemounted to hand truck 74 for storage of power cord 88. Hand truck 74 mayalso include a stair climber 90 (FIG. 4 ) to facilitate moving mainassembly 16 up a flight of stairs. In this embodiment, the manual valve92 for drain 24 is located one quarter turn around the circumference ofhousing 50, as shown, in order to make it more accessible to theoperator.

As shown in FIG. 5 , the space between the upright handles of hand truck74 conveniently mounts a panel box 94 in which the control circuitry ofmain assembly 16 is located. External power is provided to the circuitryby power cord 88, and distributed to the various components of mainassembly 16 (including vacuum source 56 and pump 60) by the circuitry.Referring now to FIG. 5A, it can be seen that panel box 94 in thisembodiment has five switches (collectively 96) that can be turned to oneof two positions. In this regard, power and water switches can be set toeither “OFF” or “ON” positions. Vacuum, air and pump switches can be setto either “REM” or “MAN” positions. When set to “MAN,” these switchesbypass relays that are otherwise controlled by a wireless unit (e.g., akey fob) carried by the operator. When set to “REM,” these switchesallow control of the relays and their associated circuits by thewireless unit. Each of the switches has an associated light(collectively 98), which illuminates when the circuit associated withthe respective switch is energized. An emergency stop button 100 cutsall power to main assembly 16 when it is depressed by the operator.

In FIGS. 6A and 6B, the outer casing of housing 50 is removed to showthe internal structure thereof. Preferably, the outer casing may beformed as a cylindrical structure that can be removed by simply slidingit up and away from the internal structure (after removal or looseningof various fasteners used to secure housing 50 together). As shown, theinternal structure of housing 50 includes a top plate 102 and a bottomplate 104 separated by a plurality of support columns. In this case,three such support columns 106A-C are spaced apart around thecircumference of plates 102 and 104. At least column 106C may be hollowto serve as a conduit for electrical wiring to the various internalcomponents.

As shown, vacuum source 56 is mounted above plate 102 so as to beoutside of the interior space of housing 50. Pump 60 is mounted insidethe interior space of housing 50 on bottom plate 104. In addition,intermediate baffle plates 108 and 110 are provided at upper and lowerpositions between plates 102 and 104. Plate 108 provides a mount forfloat switch 68, whereas plate 110 provides a mount for float switch 70.FIGS. 6A and 6B also show piping 64 for cleaning solution exiting thepump, and in-line check valve 66.

Referring specifically to FIG. 6B, an electrical distribution box 112 islocated on the upper surface of plate 102. Box 112 mates with a quickconnector to provide electrical connection between the circuitry ofpanel box 94 and the internal components of housing 50 that requireelectrical connection. As a result, all of these connections can besevered at the same time by simply separating one connector from box112. This facilitates maintenance and repair of main assembly 16, andalso provides a way (in addition to emergency stop button 100) to ceaseoperation of the apparatus quickly should it be deemed necessary by theoperator.

Various aspects of the control circuitry of main assembly 16, much ofwhich is contained in panel box 94, is shown in FIGS. 7-9 . Inparticular, FIG. 7 shows the interrelationship between the switches 96,lights 98, and emergency stop button 100. As shown, each of switches 96is in circuit with a respective relay coil (designated CR5-CR9), withthe contacts for relays CR6-CR9 being shown in FIG. 8 . A key fobcontrol circuit 114 activates other relay coils (designated CR1-CR4),the contacts for which are shown in FIG. 7 . FIG. 9 shows an additionalcircuit which may be provided to cause pulsation of the solenoid of airsupply valve 36 as discussed above.

Referring now to FIGS. 10 and 11 , a preferred embodiment of filterassembly 44 is illustrated. Like main assembly 16, filter assembly 44can be conveniently mounted on a hand truck 116 or a similar movablestructure to permit it to be easily moved from place to place. As shown,filter assembly 44 in this embodiment includes a hydrocyclonic filter118 having a container (or “bowl”) 120 into which the particulatecollects. Such filters are often used in swimming pool filtrationsystems, but have been found to be especially useful in this applicationas well. Dirty solution from drain pan 14 enters filter 118 throughinlet 122 which is fluid communication with hose 42. After passingthrough filter 118, the solution exits via outlet 124. As shown in FIG.10 , a filter flush port 126 is provided to allow the contents ofcontainer 120 to be emptied as coil cleaning is in process. In addition,filter 118 includes an air bleed port (indicated at 128).

Referring now particularly to FIG. 11 , a panel box 130 may be mountedto the back of hand truck 116 for circuitry used to control the flushingoperation. A power switch 132 connects power (supplied by a cord 133) tothe circuit components, including an interval timer 134 and a durationtimer 136. Interval timer 134 is settable by the operator to determinehow frequently the flushing operation occurs. Duration timer 136, alsosettable by the operator, determines how long the flushing operationlasts for each occurrence. For example, the flushing operation may beset to occur once every five minutes for 22 seconds each time. Duringflushing, an electrically-controlled valve 138 (which may be ball valvedriven by a solenoid) opens to allow the collected particulate to flowout of container 120 through a hose 140 and out port 126. As a result,filter 118 can continue to collect particulate matter from the usedcleaning solution without the need to stop the cleaning process. Asuitable arrangement for the flushing control circuitry is shown in FIG.12 .

FIG. 13 shows an exemplary embodiment of fluid return tool 40. As notedabove, tool 40 takes the form of a suction nozzle into which cleaningsolution is drawn at drain pan 14 after passing though filter media 48.In this embodiment, a plurality of magnets 142 are provided on the endface of tool 40 to secure it to the bottom of drain pan 14. Sufficientspace 144 is provided between the magnets 142 so that they do notsubstantially interfere with the ingress of cleaning solution.

Referring now to FIG. 14 , an exemplary nozzle device 146 is illustratedthat may be used in place of nozzle device 26 of FIG. 1 . Nozzle device146 includes a main conduit portion 148 having a suitable attachmentmechanism 150 at its proximal end. In this embodiment, the attachmentmechanism 150 comprises a cam and groove hose coupling allowing easyconnection to and disconnection from hose 30. One skilled in the artwill appreciate, however, that any suitable attachment mechanism may beutilized in accordance with the teachings of the present invention. Inthis embodiment, an elbow member 152 carrying a solution delivery face154 is located at the distal end of main conduit portion 148. (Deliveryface 154 is shown diagrammatically in FIG. 14 to better illustrate itsstructure.)

Referring now also to FIGS. 14A and 14B, it can be seen that deliveryface 154 defines a plurality of apertures (collectively 156) whichextend from one side to the other. In this case, the apertures arearranged in a grid pattern of rows and columns (e.g., seven rows andseven columns). Notably, the apertures are not parallel to the flow axisA of elbow member 152, but diverge from axis A by an angle θ (FIG. 14 ).Angle θ may often fall in a range of approximately 37 to 45 degrees(e.g., approximately 37 degrees in a preferred embodiment). As can beseen, the complement to angle θ is the angle between the direction ofthe apertures and the plane of the delivery face 154. Thus, if angle θfalls within a range of 37 to 45 degrees, the complement will fall in arange of 53 to 45 degrees. When the outer surface of delivery face 154is flat against the surface of coil unit 12, the cleaning solution willbe delivered into the fin structure so as to impinge the fins at adesired angle of attack. This maximizes both removal of material fromthe fin's surfaces and penetration of the cleaning solution deep intothe fin structure but without damaging the fins (which can be fragile).

In an alternative embodiment, the process may be enhanced by blockingoff sections of the coil and cleaning as individual smaller sections.Referring now to FIG. 15 , both sides of a channel in the coil (airentering & air leaving) may be temporarily sealed off with tape,plastic, Styrofoam insulation or other method as needed. Thisadvantageously creates an unobstructed and isolated channel betweenopposite faces of the coil.

In ordinary use, the unit is designed to allow air flow from front toback through multiple channels in the coil. Channels are formed by twoadjacent coil fins that run from the front of the coil to the back. Oncethe appropriate areas have been blocked off (creating the front and backends of the channel), suction may be applied at a rate of roughly 50-100inches water column to the front of the channel. In the same location onthe back of the coil, which is the opposite end of the channel, cleaningsolution is injected using the nozzle (and optionally a deflectorshield) as previously described. The injected cleaning solution,supplied with compressed air, simultaneously combined with the vacuumsuction on the opposite end of the channel, will remove most, if notall, of the remaining contamination.

It can thus be seen that the present invention provides a novelapparatus and method for cleaning HVAC coils. While preferredembodiments of the invention have been shown and described,modifications and variations may be made thereto by those of ordinaryskill in the art without departing from the spirit and scope of thepresent invention. In addition, it should be understood that aspects ofthe various embodiments may be interchanged both in whole or in part.Furthermore, those of ordinary skill in the art will appreciate that theforegoing description is by way of example only, and is not intended tobe limitative of the invention.

What is claimed is:
 1. An apparatus for cleaning an HVAC coil unit, saidapparatus comprising a supply and collection assembly having: a housingdefining an interior space for containing a quantity of cleaningsolution; a pump having an inlet positioned to be in fluid communicationwith the cleaning solution, said pump being operative to deliver thecleaning solution to an outlet of said supply and collection assembly ina volume of at least 40 gallons per minute (GPM); fluid return pipingdefining a conduit to conduct used cleaning solution from the HVAC coilunit back to a collection inlet; a filter assembly positioned along thefluid return piping to filter the used cleaning solution; and a fluidflow device operative to provide pressure to move a quantity of the usedcleaning solution through the fluid return piping; and the used cleaningsolution being returned to the interior space through the collectioninlet during operation of said fluid flow device.
 2. An apparatus as setforth in claim 1, wherein said fluid flow source creates negativepressure in an ullage space of the housing during operation.
 3. Anapparatus as set forth in claim 1, further comprising: a nozzle devicein fluid communication with said supply outlet via outlet piping, saidnozzle device configured to deliver the cleaning solution to a surfaceof the HVAC coil unit; a fluid return tool in fluid communication withsaid collection inlet via the return piping, said fluid return toolconfigured to collect the used cleaning solution from the HVAC coilunit.
 4. An apparatus as set forth in claim 1, wherein said filterassembly comprises a hydrocyclonic filter.
 5. An apparatus as set forthin claim 4, further comprising: an electrically-controlled flush valvein fluid communication with a collection container of said hydrocyclonicfilter; and control circuitry operative to open and close the flushvalve so as to empty the collection container.
 6. An apparatus as setforth in claim 1, further comprising air supply piping configured tointroduce compressed air into the cleaning solution being delivered fromthe supply outlet.
 7. An apparatus as set forth in claim 6, furthercomprising an electrically controlled valve in said air supply piping,said valve operative to pulsate introduction of the air into thecleaning solution at a predetermined frequency.
 8. An apparatus as setforth in claim 1, further comprising upper and lower level switches insaid interior space of said housing.
 9. An apparatus as set forth inclaim 8, wherein said upper level switch is operative to cut off powerto the pump if a threshold upper level of the cleaning solution isreached.
 10. An apparatus as set forth in claim 8, wherein said lowerlevel switch is operative to open a fresh water supply port if athreshold lower level of the cleaning solution is reached.
 11. Anapparatus as set forth in claim 1, wherein said pump is located entirelywithin said housing of said supply and collection assembly.
 12. Anapparatus as set forth in claim 11, wherein said fluid flow sourcecomprises a motor located external to said housing of said supply andcollection assembly
 13. An apparatus for cleaning HVAC cooling coils,said apparatus comprising: a supply and collection assembly having: ahousing defining an interior space for containing a quantity of cleaningsolution; a pump operative to deliver the cleaning solution to a supplyoutlet of said supply and collection assembly in a volume of at least 40gallons per minute; a fluid flow device operative to move a quantity ofused cleaning solution through return piping to a collection inlet; anozzle device in fluid communication with said supply outlet via outletpiping, said nozzle device configured to deliver the cleaning solutionto a surface of an HVAC coil unit; a fluid return tool in fluidcommunication with said collection inlet via return piping, said fluidreturn tool configured to collect the used cleaning solution from theHVAC coil unit; and a filter assembly in line with said return pipingbetween the fluid return tool and the collection inlet.
 14. An apparatusas set forth in claim 13, wherein said fluid flow source createsnegative pressure in an ullage space during operation to return the usedcleaning solution through a collection inlet.
 15. An apparatus as setforth in claim 13, wherein said filter assembly comprises ahydrocyclonic filter.
 16. An apparatus as set forth in claim 13, furthercomprising air supply piping configured to introduce compressed air intothe cleaning solution being delivered from the supply outlet.
 17. Anapparatus as set forth in claim 16, further comprising a mechanismoperative to pulsate introduction of the air into the cleaning solutionat a predetermined frequency.
 18. An apparatus as set forth in claim 17,wherein said predetermined frequency is less than approximately 36 Hz.19. An apparatus as set forth in claim 13, wherein said nozzle devicecomprises a delivery face having a substantially planar surface forjuxtaposition on the surface of the HVAC coil unit, a plurality ofapertures being defined in said delivery face for passage of thecleaning solution.
 20. An apparatus as set forth in claim 19, whereinsaid apertures are oriented at a predetermined angle relative to thesubstantially planar surface of the delivery face.
 21. An apparatus asset forth in claim 20, wherein said predetermined angle falls within arange of approximately 45 degrees to approximately 53 degrees.